Causality Aspects of Modified Kerr-Newman spacetimes

TL;DR

This paper investigates causality violations in Kerr-Newman black holes and their modified solutions, showing that parameter choices in non-commutative and f(R) gravity models can eliminate closed time-like curves and causality issues.

Contribution

It demonstrates that causality violations in Kerr-Newman spacetimes can be mitigated within modified gravity theories by appropriate parameter selection.

Findings

Causality violation regions can be eliminated by parameter choices.

Non-commutativity parameter affects the existence of Cauchy horizons.

Geodesic analysis relates to causality regions in modified spacetimes.

Abstract

In this paper, we address the problem of causality violation in the solutions of Einstein equations and seek possible causality restoration mechanisms in modifed theories of gravity. We choose for the above problem, the causality violation due to the existence of closed time-like curves in the context of Kerr-Newman black hole. We first revisit and quantify the details of the causality violation in the Kerr-Newman spacetime. We then show that the issue is also existent in two of the modified solutions to the Kerr Newman spacetime: The Non-Commutativity inspired solution and the f(R)-Gravity modifed solution. We explore the possibility of mechanisms present within the model that prevent causality violation. We show that, in both the models, the model parameters can be chosen such that the causality violating region is eliminated. We argue that in the context of non commutativity inspired solution, the non commutativity parameter can be chosen such that the causality violating region is eliminated and the inner horizon is no longer the Cauchy horizon. We then discuss the geodesic connectivity of the causality violating region in both the scenarios and quantify the geodesics that have points in the causality violating regions. We also discuss the causal aspects of Kerr Newman deSitter/antideSitter spacetimes.